电场和声场作用下微细通道流动沸腾气泡特性与传热性能

Bubble characteristics and heat transfer performance of flow boiling in microchannels under electric and ultrasound fields

为探究电场与声场对微细通道流动沸腾气泡特性以及传热性能的影响,以R141b纯制冷剂为工质,进行电场、声场、电场与声场协同作用下的传热实验。对气液两相流高速摄影图像进行拓扑特征分析,利用一维贝蒂数β_(1)与气泡数的关系、零维贝蒂数β0与受限气泡数的关系,对电场、声场作用下气泡传热特性进行定量研究。结果表明:400、600、800 V电场作用下β_(1)分别提高了23.3%、36.3%、43.1%,β0分别降低了13.6%、19.6%、23.2%,表明电场可使流动沸腾气泡数增多,受限气泡数减少,传热强化效果在800 V电场下最优,沿程传热强化系数达到1.56;在不同频率(23、40 kHz)、不同功率(12.5、50 W)声场作用下,β_(1)提高了22.7%~55.6%,β0降低了12.8%~25.8%,表明声场可使流动沸腾气泡数增多,受限气泡数减少,传热强化效果在23 kHz、50 W声场下最优,沿程传热强化系数达到1.79;电场、声场同时作用对气泡特性与传热效果的影响大于单独作用,同时作用下β_(1)提高76.2%,β0降低35.7%,沿程传热强化系数达到2.06。

In order to study the effects of electric and ultrasound fields on bubble characteristics and heat transfer performance of flow boiling in microchannels,heat transfer experiments of refrigerant R141b under different fields were studied.Quantitative research on bubble characteristics was carried out through topological analysis of high-speed photography,where the first Betti numberβ_(1)indicates the number of bubbles and the zeroth Betti numberβ0 indicates the number of confined bubbles.The results show that 400,600,800 V electric fields increaseβ_(1)by 23.3%,36.3%,43.1%and decreaseβ0 by 13.6%,19.6%,23.2%,respectively,which indicates that electric fields significantly increase the number of bubbles and decrease the number of confined bubbles.The heat transfer enhancement ratio reaches its peak at 1.56 under 800V electric field.Moreover,ultrasound fields(23,40 kHz in frequency and 12.5,50 W in power)increaseβ_(1)by the range of 22.7%to 55.6%and decreaseβ0 by the range of 12.8%to 25.8%,respectively,which indicates that ultrasound field also increases the number of bubbles and decrease the number of confined bubbles.The enhancement ratio reaches its peak at 1.79 under 23 kHz,50 W ultrasound field.Furthermore,the improvement of bubble characteristics and heat transfer performance were more obvious when two types of fields were collaboratively applied,in which caseβ_(1)increases by 76.2%andβ0 decrease by 35.7%,and the enhancement ratio reaches 2.06.